1. Field of the Invention
The present invention relates to a heat-resistant polyorganosiloxane composition.
2. Prior Art
Silicone elastomers are widely used in a variety of fields due to their excellent properties. Although such silicone elastomers have a better heat resistance than other rubbers, they still deteriorate within a short time in atmospheres hotter than 200.degree. C. due to side chain oxidation and main chain decomposition in the molecular structure. This markedly reduces their rubber properties. For this reason, prior heat-resistant silicone rubbers cannot normally be used for extended periods of time at temperatures above 250.degree. C.
For example, the addition to a polyorganosiloxane base of metal hydroxides or hydrated metal oxides, e.g., cerium hydroxide or hydrated aluminum oxide, or the addition of metal hydroxides or hydrated metal oxides and graphite, is known in the art as a means for further improving the heat resistance of flameproof room temperature-curable polyorganosiloxane compositions as described in Japanese Kokai Patent Publication No. 57-8250[1982], published Jan. 16, 1982, which is equivalent to Canadian Pat. No. 1,172,786, issued Aug. 14, 1984 to Wolfer et al, and assigned to Wacker Chemie GmbH. Another means for improving the heat resistance of silicone elastomers is the addition of iron oxide solid solutions, the ferrites, as described in Japanese Kokai Patent Publication No. 53-58557[1978], published May 26, 1978, to Toshiba Silicone KK.